Conventionally, a cordless power tool generally uses a battery pack of a nickel-cadmium battery, a nickel-hydrogen battery or the like as a drive power supply, and when the secondary battery mounted on a cordless power tool main body is exhausted, the cordless power tool is connected to a dedicated recharger, or the battery pack removed from the cordless power tool is charged and is repeatedly used (for example, see JP-UM-A-06-000679, JP-A-10-029172).
In the conventional cordless power tool, since the weight of the secondary battery relative to the main body is heavy, and charging takes time, it is desired to reduce the size and weight of the power supply and to shorten the charging time. Besides, the conventional secondary battery has a charge/discharge lifetime of approximately several hundred to one thousand cycles, which is generally shorter than the lifetime of the power tool main body, and is exchanged with a new one at the time when the performance degrades, and accordingly, the running cost becomes high.